The photographic process, in which silver halides are used, is conventionally most widely used, since it is excellent in photographic characteristics, such as sensitivity and gradation adjustment, in comparison with another photographic process, for example, electrophotography and diazo photography. The silver halide photographic process is still vigorously investigated because the highest image quality as, in particular, color hard copies can be obtained.
In recent years, from the image-formation processing method of light-sensitive materials in which silver halides are used, a system that can give an image easily and rapidly by using, for example, an instant photographic system having a built-in developing agent, or a dry-process heat-development processing using heating or the like, has been developed in place of the conventional wet process. With respect to heat-developable light-sensitive materials, "Shashin Kogaku No Kiso (Hi-ginen Shashin-hen)", published by Corona Co., p.242-, describes them, which is only directed to the black-and-white image formation method for dry silver as a representative. Various ideas about chemical reactions through which color images can be formed are reviewed in detail in Angew. Chem. Int. Ed. Engl. 1983 (22), 191-. Recently, as heat-developable color light-sensitive materials, such products as PICTROGRAPHY and PICTROSTAT (trade names) have been released from Fuji Photo Film, Co., Ltd. In the above simple and rapid processing method, a color image is formed by using a redox compound having a preformed dye attached thereto (coloring material). According to the method that uses this redox compound, an image is formed on an image-receiving sheet by the diffusion transfer process, and therefore a beautiful color image can be formed without requiring fixing of the light-sensitive material. Further, in comparison with the method in which a dye is formed by the coupling reaction between the oxidized product of a developing agent and a coupler, which method is most generally carried out in the field of photography, in the method that uses the redox compound, a color light-sensitive material advantageous in color reproduction can be designed, since a dye to give a preferable hue can be chosen in advance.